1. Field of the Invention
The invention concerns a method for manufacturing a cement clinker in a facility as well as a facility for manufacturing a cement clinker as such.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Manufacturing a cement clinker most often uses a so-called dry baking process, where the previously crushed raw materials are calcinated in a rotary furnace. So as to reduce the energy requirements of the operation, exchangers have been added upstream and downstream of the rotary furnace and directly recover the heat contained in the materials and the fumes coming out of the furnace. Thus, whereas the products coming out of the furnace have a temperature greater than 1,000° C., the hot gas, air or fume flows, coming out of these exchangers, although they are not used for the baking operation, are then only at temperatures lower than 350° C. However, these gases still contain an amount of heat which may represent 20 to 30% of the energy introduced in the form of fuel in the facility.
The hot gases are generally used for drying the raw materials for the manufacture of the clinker. However, only a portion of the heat is necessary for the drying operations except for a very rare case where the humidity of the materials is very high. A portion of the unused hot gases thus provides available energy.
Lost heat recovery at the end of the power production process is then known and performed in many factories. The most current method comprises directing the hot gases towards exchangers formed of tubes wherein water circulates that heat transforms into pressurised steam for moving the turbines of a electric power generator. Due to the moderate temperature of the gases in the exchangers, the overall energy conversion yield into electricity is low.
As a means to improve exchangers performance, it is known to replace water with pentane, for instance. In spite of such improvement, the yield does not exceed 17% which is significantly smaller than the yield of a conventional electric power thermal plant.
For improving the recovery yield substantially, a so-called co-generation method is then known, which comprises increasing the work temperature thanks to additional fuel uptake. Thus, for example, not only the amount of recovered energy is increased, but the conversion yield is also improved thanks to temperature elevation.
As most cement facilities use solid fuels such as coal, oil coke, it is necessary to have a significant combustion volume for optimal combustion of the excess fuel and thereby to have a combustion chamber of appropriate size, i.e. large enough. Using such a combustion chamber moreover requires to evacuate the ashes therefrom, and also presents the shortcoming of generating larger quantities of NOx gas.
For instance, documents EP-0.492.133 and CB 1601214 disclose such cement facilities wherein combustion energy is recovered to produce electricity.
Document EP-0.045.811 discloses a method for recovering exhaust gases from a boiler in a electric power generator device using a combustible material such as fuel. This document more particularly handles exhaust gases processing which is performed in a preheating section in a facility for manufacturing a cement clinker.
Hot air generated by the clinker cooler of the facility is sent via a duct up to said boiler for use as combustion gas. The combustible material is injected in the duct in a region adjacent to the inlet to the boiler, in particular in the form of pulverised coal.
The aim of the present invention is to remedy the drawbacks aforementioned while offering a method for manufacturing a cement clinker in a facility as well as a facility for manufacturing a cement clinker as such, for increasing the energy recovery yields by minimising the fuel uptake necessary to cogeneration.
Other aims and advantages will appear in the following description, which is given only by way of example, and without being limited thereto.